The role of sorption and bacteria in mercury partitioning and bioavailability in artificial sediments

This study compared the relative importance of three types of sorption (organic matter-particle, mercury-organic matter and mercury-particle) in controlling the overall mercury partitioning and bioavailability in sediments. We found that all three types of sorption were important for both inorganic mercury (Hg) and methylated mercury (MeHg). Mercury-particle sorption was more important than mercury-fulvic acid (FA) sorption in increasing the mercury concentrations with increasing aging. Bioavailability (quantified by gut juice extraction from sipunculans) was mainly controlled by mercury-particle sorption, while FA-particle and mercury-FA sorption were not as important, especially for MeHg. Bacterial activity also increased the partitioning of Hg or MeHg in the sediments and was further facilitated by the presence of organic matter. The bioavailability of Hg or MeHg from sediments was only slightly influenced by bacterial activity. This study highlights the importance of sorption from various sources (especially mercury-particle sorption) as well as bacteria in controlling the partitioning and bioavailability of Hg or MeHg in sediments.     

Influence of titanium dioxide nanoparticles on speciation and bioavailability of arsenite

In this study, the influence of the co-existence of TiO₂ nanoparticles on the speciation of arsenite [As(III)] was studied by observing its adsorption and valence changing. Moreover, the influence of TiO₂ nanoparticles on the bioavailability of As(III) was examined by bioaccumulation test using carp (Cyprinus carpio). The results showed that TiO₂ nanoparticles have a significant adsorption capacity for As (III). Equilibrium was established within 30 min, with about 30% of the initial As (III) being adsorbed onto TiO₂ nanoparticles. Most of aqueous As (III) was oxidized to As(V) in the presence of TiO₂ nanoparticles under sunlight. The carp accumulated considerably more As in the presence of TiO₂ nanoparticles than in the absence of TiO₂ nanoparticles, and after 25-day exposure, As concentration in carp increased by 44%. Accumulation of As in viscera, gills and muscle of the carp was significantly enhanced by the presence of TiO₂ nanoparticles.     

Toxicity of arsenate and arsenite on germination, seedling growth and amylolytic activity of wheat

Effects of different concentrations of arsenite and arsenate (0-16 mg/l) on seed germination, relative root length and shoot height, arsenic accumulation in young seedlings, alpha-amylase, beta-amylase and total amylolytic activity in wheat were investigated in order to elucidate the toxicity of arsenic in the early developmental stage. Germination percentages of different wheat varieties had different responses to arsenic species and decreased significantly with increasing arsenic concentrations except Duokang 1. Relative root length (RRL) and relative shoot height (RSH) of wheat seedlings decreased with increasing concentrations of arsenite and arsenate. The relative root lengths were correlated with the relative shoot heights for arsenite (r2 = 0.79) and arsenate (r2 = 0.77). Arsenic uptake by seedlings increased with the increasing concentrations of arsenite or arsenate and followed the Michaelis-Menten kinetics function. The average total amylolytic activity and beta-amylase activity had no significant difference comparable to that of controls at the concentration 2 mg/l arsenite or arsenate, but decreased apparently when the concentration was higher than 2 mg/l. Whereas the alpha-amylase activity decreased with increasing concentrations of arsenite or arsenate over the whole concentration range. Arsenite decreased all the endpoints more remarkably than arsenate. In comparison, shoot height and root length were more sensitive to arsenic than other endpoints and might be used as indicators for arsenic toxicity.     

Influence of natural dissolved organic carbon on the bioavailability of mercury to a freshwater alga

Bioavailability of mercury (Hg) to Selenastrum capricornutum was assessed in bioassays containing field-collected freshwater of varying dissolved organic carbon (DOC) concentrations. Bioconcentration factor (BCF) was measured using stable isotopes of methylmercury (MeHg) and inorganic Hg(II). BCFs for MeHg in low-DOC lake water were significantly larger than those in mixtures of lake water and high-DOC river water. The BCF for MeHg in rainwater (lowest DOC) was the largest of any treatment. Rainwater and lake water also had larger BCFs for Hg(II) than river water. Moreover, in freshwater collected from several US and Canadian field sites, BCFs for Hg(II) and MeHg were low when DOC concentrations were >5mg L(-1). These results suggest high concentrations of DOC inhibit bioavailability, while low concentrations may provide optimal conditions for algal uptake of Hg. However, variability of BCFs at low DOC indicates that DOC composition or other ligands may determine site-specific bioavailability of Hg.     

抗砷菌对蜈蚣草生长及其砷吸收能力的影响

从湖南某砷污染地区挖取蜈蚣草,在蜈蚣草根系与根系新鲜土中筛选出11组抗砷菌单菌落(依次编号为A、B、C、D…K),并将其接种到蜈蚣草盆栽试验中,研究抗砷菌对蜈蚣草生长以及对砷吸收能力的影响。结果表明,抗砷菌在一定程度上能够刺激蜈蚣草的生长,尤其是根内筛选抗砷菌明显提高了蜈蚣草的生物量。其中,E、G抗砷菌可以增强蜈蚣草对砷的吸收能力,促进砷由蜈蚣草地下部分向地上部分转移。测定接种E、G抗砷菌的蜈蚣草各部位抗逆性指标的含量,得出E、G抗砷菌能减轻蜈蚣草根系质膜的损伤,提高蜈蚣草根系抗砷胁迫的能力。对E抗砷菌进行鉴定,该菌属于半知菌纲,丛梗胞目,丝核菌属(Rhizoctoniasp.),为内生菌根菌,该菌可产生类似赤霉素的活性物质,从而促进植物生长。     

A theory on the mechanisms regulating the bioavailability of mercury in natural waters

A number of quantifiable properties of natural waters have been used by various scientists to 'explain' the Hg content in fish (e.g. pH, level of bioproduction, humosity, conductivity, calcium content, oxygen conditions, zinc and selenium content). This work presents a theory aimed at providing an explanation of the chemical mechanisms behind many established statistical relationships. The theory focuses on some equilibrium reactions and the causal relationships behind these reactions. The basic concept of the theory is that the activity of Hg(2+) in natural waters is essentially regulated by the activity of S(2-), which, in turn, is strongly affected by pH and redox conditions. Due to protonisation reactions, the S(2-) activity is very low at natural pH levels. The equilibrium between Hg(2+) and HgS(s) is given by the solubility constant Ks = 10(-52). This is an extremely low constant, which indicates that, in the presence of sulphide, essentially all Hg will appear as HgS(s). The Hg(2+) activity, and the Hg content in fish, can be increased if the S(2-) activity is decreased by lowering the pH and/or increasing the redox potential. Besides sulphide there are two other elements with a similar relationship towards Hg; namely, Se and Te (Ks = 10(-58) and Ks = 10(-70), respectively). The Hg(2+) concentration in natural waters varies quite widely, but is often about 5 ng litre(-1). This is a high concentration in these contexts. Such as high concentration can prevail only if the S(2-) (and/or the Se(2-)) activity is very small. In waters where the S(2-) and/or the Se(2-)) activity is high, e.g. from sulphide rocks in the drainage area, or if S(2-) and/or Se(2-) are added to the water, the Hg(2+) activity, and the Hg content in fish, will be effectively reduced.     

Effects of sediment composition on inorganic mercury partitioning, speciation and bioavailability in oxic surficial sediments

Artificially prepared sediments were used to assess the effects of sediment composition on inorganic Hg partitioning, speciation and bioavailability. Organic coating in sediment greatly increased the Hg partitioning and the amount of bioavailable Hg bound with the clay and the Fe and Mn oxides, but had little effect on that bound with the quartz and calcium carbonate as a result of weaker binding of humic acids and fulvic acids. The clay content increased the concentration of Hg in the sediments but inhibited the gut juice extraction due to the strong binding of Hg-organic matter (OM) complexes. Most Hg in the sediments was complexed by OM (mainly distributed in the organo-complexed phase and the strongly complexed phase), and the Hg-OM complexes (especially Hg in the strongly complexed phase) in sediments contributed much to gut juice extraction. Redistribution of Hg-OM complexes between sediments and gut juices may occur during gut juice extraction and modify Hg bioavailability and speciation in sediments.     

Toxicity of twenty-two plant essential oils against pathogenic bacteria of vegetables and mushrooms

Toxicity of twenty-two essential oils to three bacterial pathogens in different horticultural systems: Xanthomonas campestris pv. phaseoli (causing blight of bean), Clavibacter michiganensis subsp. michiganensis (bacterial wilt and canker of tomato), and Pseudomonas tolaasii (causal agent of bacterial brown blotch on cultivated mushrooms) was tested. Control of bacterial diseases is very difficult due to antibiotic resistance and ineffectiveness of chemical products, to that essential oils offer a promising alternative. Minimal inhibitory and bactericidal concentrations are determined by applying a single drop of oil onto the inner side of each plate cover in macrodilution assays. Among all tested substances, the strongest and broadest activity was shown by the oils of wintergreen (Gaultheria procumbens), oregano (Origanum vulgare), and lemongrass (Cymbopogon flexuosus. Carvacrol (64.0–75.8%) was the dominant component of oregano oils, while geranial (40.7%) and neral (26.7%) were the major constituents of lemongrass oil. Xanthomonas campestris pv. phaseoli was the most sensitive to plant essential oils, being susceptible to 19 oils, while 11 oils were bactericidal to the pathogen. Sixteen oils inhibited the growth of Clavibacter michiganensis subsp. michiganensis and seven oils showed bactericidal effects to the pathogen. The least sensitive species was Pseudomonas tolaasii as five oils inhibited bacterial growth and two oils were bactericidal. Wintergreen, oregano, and lemongrass oils should be formulated as potential biochemical bactericides against different horticultural pathogens.     

Toxicity evaluation of reactive dyestuffs, auxiliaries and selected effluents in textile finishing industry to luminescent bacteria Vibrio fischeri

The toxicity of 17 selected process effluents, 11 reactive dyestuffs and 8 auxiliaries from a textile dyeing and finishing mill in Ayazaga, Istanbul, Turkey was evaluated by bioluminescence test using bacteria Vibrio fischeri in LUMIStox 300. The EC20 and EC50 for auxiliaries, the EC20 for dyestuffs were determined. For selected process effluents GL-values, the dilution level at which a wastewater sample causes less than 20% inhibition, were examined. Our results demonstrate that the toxicity assessment with luminescent bacteria is effective and of practical use for chemicals applied in textile finishing industry with the limitation of the deep dark-colored dye bath samples and for the related effluents. Inhibition effects of numerous dyestuffs as well as auxiliaries to luminescent bacteria differed considerably with a range 5-600 mg l(-1) for EC20 and 9-6930 mg l(-1) for EC50, respectively. Among 17 effluents, I sample exhibited high toxicity (GL = 100), 7 showed moderate toxicity (GL = 12-32), and 9 had a GL-value <10 indicating a low or no toxicity.     

Tracking mercury in the southwestern Atlantic Ocean: the use of tuna and tuna-like species as indicators of bioavailability

Mercury is a trace element that is potentially dangerous due its high toxicity and tendency to bioaccumulate in organisms. Currently, high mercury concentrations are seen in the environment especially due climate changes. Studies regarding mercury bioavailability in the southwestern Atlantic Ocean using tuna and tuna-like species are rare. The aim of the present study was to use tuna and tuna-like species (Thunnus atlanticus, Thunnus albacares, Katsuwonus pelamis, Euthynnus alletteratus, Coryphaena hippurus and Sarda sarda) as indicators of the availability of total mercury (THg) in oceanic food webs of the southwestern Atlantic Ocean. THg concentrations varied significantly among species for both muscle and liver (Kruskal–Wallis test; H5,130 = 52.7; p < 0.05; H5,130 = 50.1; p < 0.05, respectively). The lowest concentrations were found in C. hippurus (0.008 mg kg−1 wet weight in the muscle and 0.003 mg kg−1 wet weight in the liver), and the highest concentrations were reported in the muscle of T. atlanticus (1.3 mg kg−1 wet weight) and in the liver of S. sarda (2.5 mg kg−1 wet weight). The continued monitoring of tuna and tuna-like species is necessary to assist in their conservation since tuna can be sentinels of mercury pollution.     

Application of phosphate-solubilizing bacteria for enhancing bioavailability and phytoextraction of cadmium (Cd) from polluted soil

In this study, phosphate-solubilizing bacteria (PSB), Bacillus megaterium, were used to enhance Cd bioavailability and phytoextractability of Cd from contaminated soils. This strain showed a potential for directly solubilizing phosphorous from soils more than 10 folds greater than the control without inoculation. The results of pot experiments revealed that inoculation with B. megaterium significantly increased the extent of Cd accumulation in Brassica juncea and Abutilon theophrasti by two folds relative to the uninoculated control. The maximum Cd concentrations due to inoculation were 1.6 and 1.8 mg Cd g⁻¹ plant for B. juncea and A. theophrasti after 10 wk, respectively. The total biomass of A. theophrasti was not significantly promoted by the inoculation treatment, yet the total biomass of B. juncea increased from 0.087 to 0.448 g. It is also worth to mention that B. juncea predominantly accumulates Cd in its stems (39%) whereas A. theophrasti accumulates it in its leaves (68%) after 10 wk. The change of the Cd speciation indicated that inoculation of B. megaterium as PSB increased the bioavailabilty of Cd and consequently enhanced its uptake by plants. The present study may provide a new insight for improving phytoremediation using PSB in the Cd-contaminated soils.     

Inhibition of rainbow trout acetylcholinesterase by aqueous and suspended particle-associated organophosphorous insecticides

Cadmium (Cd) adsorption on 14 non-calcareous New Jersey soils was investigated with a batch method. Both adsorption edge and isotherm experiments were conducted covering a wide range of soil composition, e.g. soil organic carbon (SOC) concentration ranging from 0.18% to 7.15%, and varying Cd concentrations and solution pH. The SOC and solution pH were the most important parameters controlling Cd partition equilibrium between soils and solutions in our experimental conditions. The Windermere humic aqueous model (WHAM) was used to calculate Cd adsorption on soils. The effect of solution chemistry (various pH and Cd concentrations) on Cd adsorption can be well accounted for by WHAM. For different soil compositions, SOC concentration is the most important parameter for Cd binding. Only a fraction of SOC, the so-called active organic carbon (AOC), is responsible for Cd binding. We found a linear relationship between SOC and AOC based on the adsorption edge data. The linear relationship was validated by the independent data sets: adsorption isotherm data, which presumably can be used to predict Cd partition equilibrium across a wide range of soil compositions. The modeling approach presented in this study helps to quantitatively predict Cd behavior in the environment.     

Toxicity of nanosized and bulk ZnO, CuO and TiO2 to bacteria Vibrio fischeri and crustaceans Daphnia magna and Thamnocephalus platyurus

As the production of nanoparticles of ZnO, TiO2 and CuO is increasing, their (eco)toxicity to bacteria Vibrio fischeri and crustaceans Daphnia magna and Thamnocephalus platyurus was studied with a special emphasis on product formulations (nano or bulk oxides) and solubilization of particles. Our innovative approach based on the combination of traditional ecotoxicology methods and metal-specific recombinant biosensors allowed to clearly differentiate the toxic effects of metal oxides per se and solubilized metal ions. Suspensions of nano and bulk TiO2 were not toxic even at 20 g l(-1). All Zn formulations were very toxic: L(E)C50 (mg l(-1)) for bulk ZnO, nanoZnO and ZnSO4.7H2O: 1.8, 1.9, 1.1 (V. fischeri); 8.8, 3.2, 6.1 (D. magna) and 0.24, 0.18, 0.98 (T. platyurus), respectively. The toxicity was due to solubilized Zn ions as proved with recombinant Zn-sensor bacteria. Differently from Zn compounds, Cu compounds had different toxicities: L(E)C50 (mg l(-1)) for bulk CuO, nano CuO and CuSO4: 3811, 79, 1.6 (V. fischeri), 165, 3.2, 0,17 (D. magna) and 95, 2.1, 0.11 (T. platyurus), respectively. Cu-sensor bacteria showed that toxicity to V. fischeri and T. platyurus was largely explained by soluble Cu ions. However, for Daphnia magna, nano and bulk CuO proved less bioavailable than for bacterial Cu-sensor. This is the first evaluation of ZnO, CuO and TiO2 toxicity to V. fischeri and T. platyurus. For nano ZnO and nano CuO this is also a first study for D. magna.     

Influence of bacteria on Pb and Zn speciation, mobility and bioavailability in soil: A laboratory study

A soil column experiment was carried out to investigate the effects of inoculation of bacteria on metal bioavailability, mobility and potential leachability through single chemical extraction, consequential extraction and in situ soil solution extraction technologies. Results showed that bacteria inoculated, including Azotobacter chroococcum, Bacillus megaterium and Bacillus mucilaginosus, may pose both positive and negative impacts on bioavailability and mobility of heavy metals in soil, depending on the chemical nature of the metals. The activities of bacteria led to an increase of water dissolved organic carbon (DOC) concentration and a decrease of pH value, which enhanced metal mobility and bioavailability (e.g. an increase of water-soluble and HOAc-soluble Zn). On the other hand, bacteria could immobilize metals (e.g. a great reduction of water-soluble Pb) due to the adsorption by bacterial cell walls and possible sedimentation reactions with phosphate or other anions produced through bacterial metabolism.     

Toxicity monitoring and classification of endocrine disrupting chemicals (EDCs) using recombinant bioluminescent bacteria

A recombinant bioluminescent Escherichia coli, DPD2794, containing the recA promoter region fused to luxCDABE originating from Vibrio fischeri was used for detecting genotoxicity caused by endocrine disrupting chemicals (EDCs) to cells. As well, several other recombinant bioluminescent bacteria, including TV1061, which is sensitive to protein damage (grpE::luxCDA BE), DPD2511, sensitive to oxidative damage (katG::luxCDABE), and DPD2540, sensitive to membrane damage (fabA::luxCDABE), were used for evaluating other possible modes of toxicity. It was found that the recombinant bacteria could monitor the toxic effect, not estrogenic effect, due to the presence of various EDCs through the measurement of bioluminescence (BL) and cell growth rate, which depend upon the type of toxicity occurring and which of the four strains was used. In addition, it was found that the damage caused by EDCs can be classified into several groups upon their mechanisms of toxic action.     

Toxicity of 58 substituted anilines and phenols to algae Pseudokirchneriella subcapitata and bacteria Vibrio fischeri: comparison with published data and QSARs

A congeneric set of 58 substituted anilines and phenols was tested using the 72-h algal growth inhibition assay with Pseudokirchneriella subcapitata and 15-min Vibrio fischeri luminescence inhibition assay. The set contained molecules substituted with one, two or three groups chosen from -chloro, -methyl or -ethyl. For 48 compounds there was no REACH-compatible algal toxicity data available before. The experimentally obtained EC50 values (mg L⁻¹) for algae ranged from 1.43 (3,4,5-trichloroaniline) to 197 (phenol) and for V. fischeri from 0.37 (2,3,5-trichlorophenol) to 491 (aniline). Only five of the tested 58 chemicals showed inhibitory effect to algae at concentrations >100 mg L⁻¹, i.e. could be classified as “not harmful”, 32 chemicals as “harmful” (10-100 mg L⁻¹) and 21 as “toxic” (1-10 mg L⁻¹). The occupied para-position tended to increase toxicity whereas most of the ortho-substituted congeners were the least toxic. As a rule, the higher the number of substituents the higher the hydrophobicity and toxicity. However, in case of both assays, the compounds of similar hydrophobicity showed up to 30-fold different toxicities. There were also assay/organism dependent tendencies: phenols were more toxic than anilines in the V. fischeri assay but not in the algal test. The comparison of the experimental toxicity data to the data available from the literature as well as to QSAR predictions showed that toxicity of phenols to algae can be modeled based on hydrophobicity, whereas the toxicity of anilines to algae as well as toxicity of both anilines and phenols to V. fischeri depended on other characteristics in addition to logK_ow.     

Importance of sulfate reducing bacteria in mercury methylation and demethylation in periphyton from Bolivian Amazon region

Sulfate reducing bacteria (SRB) are important mercury methylators in sediments, but information on mercury methylators in other compartments is ambiguous. To investigate SRB involvement in methylation in Amazonian periphyton, the relationship between Hg methylation potential and SRB (Desulfobacteraceae, Desulfobulbaceae and Desulfovibrionaceae) abundance in Eichhornia crassipes and Polygonum densiflorum root associated periphyton was examined. Periphyton subsamples of each macrophyte were amended with electron donors (lactate, acetate and propionate) or inhibitors (molybdate) of sulfate reduction to create differences in SRB subgroup abundance, which was measured by quantitative real-time PCR with primers specific for the 16S rRNA gene. Mercury methylation and demethylation potentials were determined by a stable isotope tracer technique using ²⁰⁰HgCl and CH₃²⁰²HgCl, respectively. Relative abundance of Desulfobacteraceae (<0.01-12.5%) and Desulfovibrionaceae (0.01-6.8%) were both highly variable among samples and subsamples, but a significant linear relationship (p < 0.05) was found between Desulfobacteraceae abundance and net methylmercury formation among treatments of the same macrophyte periphyton and among all P. densiflorum samples, suggesting that Desulfobacteraceae bacteria are the most important mercury methylators among SRB families. Yet, molybdate only partially inhibited mercury methylation potentials, suggesting the involvement of other microorganisms as well. The response of net methylmercury production to the different electron donors and molybdate was highly variable (3-1104 pg g⁻¹ in 12 h) among samples, as was the net formation in control samples (17-164 pg g⁻¹ in 12 h). This demonstrates the importance of community variability and complexity of microbial interactions for the overall methylmercury production in periphyton and their response to external stimulus.     

TiO2-catalyzed photooxidation of arsenite to arsenate in aqueous samples

The TiO2-catalyzed photooxidation of arsenite (As(III)) to arsenate (As(V)) was studied in aqueous TiO2 suspensions using a solar simulator which emitted ultraviolet and visible radiations. The concentration of As(III) was varied between 50 microg l(-1) and 10 mg l(-1), and the concentration of TiO2 between 1 mg l(-1) and 50 mg l(-1). Total oxidation of As(III) to As(V) occurred within minutes. The concentration of As(III) declined exponentially which indicates first-order kinetics. In the pH range between 5 and 9 there was no significant influence of the pH of the suspension on the reaction rate. Batch experiments without irradiation showed that part of the arsenic was adsorbed on the TiO2 surface. When using 100 microg l(-1) As and between 1 mg l(-1) and 50 mg l(-1) TiO2, 8-39% of As(III) and up to 73% of As(V) were adsorbed by TiO2. As(III) was also oxidized by UV radiation in the absence of TiO2, but the reaction was slower than in the presence of TiO2 resulting in an irradiation time too long for practical use. In addition, oxidation of As(III) in the presence of TiO2 was also observed under solar irradiation within a few minutes.     

Modeling the photo-oxidation of dissolved organic matter by ultraviolet radiation in freshwater lakes: implications for mercury bioavailability

Uncertainties in projected ultraviolet (UV) radiation may lead to future increases in UV irradiation of freshwater lakes. Because dissolved organic carbon (DOC) is the main binding phase for mercury (Hg) in freshwater lakes, an increase in DOC photo-oxidation may affect Hg speciation and bioavailability. We quantified the effect of DOC concentration on the rate of abiotic DOC photo-oxidation for five lakes (DOC=3.27-12.3 mg L(-1)) in Kejimkujik National Park, Canada. Samples were irradiated with UV-A or UV-B radiation over a 72-h period. UV-B radiation was found to be 2.36 times more efficient at photo-oxidizing DOC than UV-A, with energy-normalized rates of dissolved inorganic carbon (DIC) production ranging from 3.8×10(-5) to 1.1×10(-4) mg L(-1)J(-1) for UV-A, and from 6.0×10(-5) to 3.1×10(-4) mg L(-1)J(-1) for UV-B. Energy normalized rates of DIC production were positively correlated with DOC concentrations. Diffuse integrated attenuation coefficients were quantified in situ (UV-A K(d)=0.056-0.180 J cm(-1); UV-B K(d)=0.015-0.165 J cm(-1)) and a quantitative depth-integrated model for yearly DIC photo-production in each lake was developed. The model predicts that, UV-A produces between 3.2 and 100 times more DIC (1521-2851 mg m(-2) year(-1)) than UV-B radiation (29.17-746.7 mg m(-2) year(-1)). Future increases in UV radiation may increase DIC production and increase Hg bioavailability in low DOC lakes to a greater extent than in high DOC lakes.